Bactericidal activity of peroxynitrite.

Peroxynitrite is a strong oxidant formed by macrophages and potentially by other cells that produce nitric oxide and superoxide. Peroxynitrite was highly bactericidal, killing Escherichia coli in direct proportion to its concentration with an LD50 of 250 microM at 37 degrees C in potassium phosphate, pH 7.4. The apparent bactericidal activity of a given concentration peroxynitrite at acidic pH was less than that at neutral and alkaline pH. However, after taking the rapid pH-dependent decomposition of peroxynitrite into account, the rate of the killing was not significantly different at pH 5 compared to pH 7.4. Metal chelators did not decrease peroxynitrite-mediated killing, indicating that exogenous transition metals were not required for toxicity. The hydroxyl radical scavengers mannitol, ethanol, and benzoate did not significantly affect toxicity while dimethyl sulfoxide enhanced peroxynitrite-mediated killing. Dimethyl sulfoxide is a more efficient hydroxyl radical scavenger than the other three scavengers and increased the formation of nitrogen dioxide from peroxynitrite. In the presence of 100 mM dimethyl sulfoxide, 60.0 +/- 0.3 microM nitrogen dioxide was formed from 250 microM peroxynitrite as compared to 2.0 +/- 0.1 microM in buffer alone. Thus, formation of nitrogen dioxide may have enhanced the toxicity of peroxynitrite decomposing in the presence of dimethyl sulfoxide.     

Molecular thermodynamic model to predict the alpha-helical secondary structure of polypeptide chains in solution.

The native state of a protein molecule in aqueous solutions represents one of the lowest states of Gibbs energy [Anfinsen, C.B. (1973) Science 181, 223-230]. Much progress has been made about the rules of protein folding [King, J. (1989) Chem. Eng. News 67, 32-54] and the dominant forces in protein folding [Dill, K.A. (1990) Biochemistry 29, 7133-7155]. However, the quantitative contributions of different Gibbs energy terms to protein stability remains a controversial issue [Moult, J., & Unger, R. (1991) Biochemistry 30, 3816-3824]. A molecular thermodynamic model has been proposed for the Gibbs energy of folding a residue in aqueous homopolypeptides from a random-coiled state to either the alpha-helix state or the beta-sheet state [Chen, C.-C., Zhu, Y., King, J.A., & Evans, L.B. (1992) Biopolymers 32, 1375-1392]. In this work, we present a generalization of the molecular thermodynamic model for the Gibbs energy of folding natural and synthetic heteropolypeptides from random-coiled conformations into alpha-helical conformations. The generalized model incorporates the intrinsic folding potential due to residue-solvent interactions, the cooperative folding effect due to residue-residue interactions, and the location and length of alpha-helices. The utility of the model was demonstrated by examining the stability of alpha-helical conformations of a number of natural polypeptides including C-peptide (residues 1-13) and S-peptide (residues 1-20) of RNase A (bovine pancreatic ribonuclease A), the P alpha fragment in BPTI (bovine pancreatic trypsin inhibitor), and synthetic polypeptides (the copolymers of different amino acid residues) including alanine-based peptides (16 or 17 residues long) in water. The computed Gibbs energies correspond well with the experimental data on helicity. The results also accounted for the effects of amino acid substitution and temperature on the stability of alpha-helical conformations of the test polypeptides.     

元江干热河谷肉质多利灌丛的研究

以内质多刺植物霸王鞭(Euphorbia royleana)和仙人掌(Opuntia monacantha)为特征的具有荒漠植被景观的元江干热河谷肉质多刺灌丛是一种特殊的次生植被,是在近代原生植被的强烈破坏下,栽培逸生的霸王鞭和仙人掌在局部特别千热土薄多石之处发展而形成的。该群落外貌和结构特殊,可初步定为一个群丛,下分两个亚群丛。在种类组成上,该群落与热带亚洲干早植物区系联系密切,在区系起源上具有古南大陆残余背景,在群落形成和发展上又与人为活动相联系。     

中国大白蚁亚科壤白蚁新属新种（等翅目：白蚁科）

壤白蚁属Parahy potermes Zhu et Huang,新属 模式种:曼允壤白蚁Parahy potermes manyunensis,新种。 属征:兵蚁头近卵圆形,头背面被毛稀少,两侧缘于触角前骤然狭缩,头中部最宽,后缘宽圆,头背面中部明显隆起;左上颚内缘中部第1缘齿上方具2—3枚小齿。 比较与讨论:本新属与地白蚁属Hypotermes Holmgren较接近。但Hypotermes头两侧缘触角前不呈狭缩状;左上颚第1缘齿上方不具锯齿状小齿;头背面中部呈弧状隆起。     

Efficient translocation of positively charged residues of M13 procoat protein across the membrane excludes electrophoresis as the primary force for membrane insertion.

The coat protein of bacteriophage M13 is inserted into the Escherichia coli plasma membrane as a precursor protein, termed procoat, with a typical leader peptide of 23 amino acid residues. Its membrane insertion requires the electrochemical potential but not the cellular components SecA and SecY. Since the electrochemical gradients result in the periplasmic side of the membrane being positively charged, the membrane potential could contribute to the transfer of the negatively charged central region of procoat across the membrane. Here we demonstrate that the central domain following the leader peptide can be translocated across the membrane even when the net charge of the region is changed from -3 to +3. This rules out an electrophoresis-like insertion mechanism for procoat. We also show that the sec independence of procoat insertion is linked to the presence of the second apolar domain. The deletion of most of the second apolar domain from a procoat fusion protein results in sec dependent membrane insertion of the hybrid protein. Moreover, like other proteins that require the sec genes, translocation of this sec dependent procoat protein is inhibited when positively charged residues are introduced after the leader peptide. Loop models involving one or two hydrophobic regions are presented that account for the differences in tolerance of positively charged residues.     

急性缺氧性缺氧时心脏功能的改变

F_(IO_2)(吸入气氧浓度)为12.35、9.87及7.7l％,分别吸入10、8及5min时,心功能呈代偿性增强改变。F_(IO_2)为9.37％、吸入20min时心功能的变化趋势与9.87％8min时仍基本相同。继发性缺二氧化碳对缺氧引起的心功能代偿性增强,在一定程度上起抵消作用。F_(IO_2)为9.87％时的缺氧程度约相当于18km高空加压供氧总压值为15.3kPa(115mmHg)时的缺氧。单纯从缺氧因素考虑,将总压值由常用的17.3kPa(130mmHg)降低为15.3kPa是可允许的。     

冬虫夏草多糖的分子结构与免疫活性

 冬虫夏草多糖(在本文中名为CS-81002)是由冬虫夏草菌Cordyceps sinensis(Berk)Sacc在人工发酵条件下产生的胞外多糖。用凝胶过滤法测出CS-81002的分子量Mr=43kD。CS-81002的单糖组成为Man:Gal:Glc=10.3:3.6:1。甲基化分析和部份酸水解结果表明,CS-81002是多分支的杂多糖,由→6)-Manp-(1→形成主链,大约每10个主链Man残基中,有6个在C3位上被取代(即形成→3,6)-Manp-(1→分支),有4个在位C2上被取代(即形成→2,6-Manp-(1→分支),从而形成侧链。主链中还有少许未被取代的Man残基。侧链则由→3-)-Galf-(1→,→4)-Glcf-(1→,→4)-Manp-(1→和→2)-Manp-(1→组成。位于非还原末端的,则三种单糖残基都有。CS-81002在5mg/kg体重×12剂量条件下,对正常的昆明小鼠腹腔巨噬细胞吞噬功能有显著促进作用。在同样剂量条件下,对正常LACA小鼠脾脏溶血斑形成细胞(PFC)对绵羊红细胞的溶血作用无显著影响。不同程度的部份酸水解可使CS-81002的分子量下降,分支减少,并且对巨噬细胞吞噬功能的促进作用亦有下降趋势。在所得到的各个部份酸水解级分(分子量分别为41000,40000,32000,16000和12000)中,分子量为12000的级分对巨噬细胞吞噬功能无促进作用。     

El Tor型霍乱弧菌及其细胞壁缺陷型分子遗传学背景的研究

El Tor 型霍乱弧菌(以下简称 El Tor 弧菌)可以在人工培养条件下长期存活。当微环境改变时可形成细胞壁有不同程度缺陷的菌株如抗噬菌体突变株或 L 型菌株。我们以 DNA 酶切图谱和 El Tor 弧菌溶血素、神经氨酸酶基因探针杂交图谱为参数对 El Tor 弧菌的野生型及其细胞壁缺陷型变异株在遗传背景上进行了比较分析研究。结果提示细胞壁缺陷型菌株与其野生型在DNA 水平上高度同源。此外,文中还介绍了一种从 L 型菌株中制备 DNA 的方法。     

Time-Dependent Increase in Protein Phosphorylation Following One-Trial Enhancement in Hermissenda

Abstract: One-trial conditioning of the nudibranch mollusk Hermissenda produces short- and long-term changes in excitability (enhancement) of identified sensory neurons. To investigate the biochemical mechanisms underlying this example of plasticity, we have examined changes in protein phosphorylation at different times following the in vitro conditioning trial. Changes in the incorporation of ³²PO₄ into proteins were determined using two-dimensional polyacrylamide gel electrophoresis, autoradiography, and densitometry. Conditioning resulted in increases in levels of several phosphoproteins, five of which, ranging in apparent molecular mass from 22 to 55 kDa, were chosen for analysis. The increased phosphorylation of the 46- and 55-kDa phosphoproteins detected 2 h postconditioning was significantly greater than the level of phosphorylation detected in an unpaired control group, indicating that long-term enhancement is pairing specific. Statistically significant increases in phosphorylation as compared with the control group that received only light were detected immediately after conditioning (5 min) for the 55-, 46-, and 22-kDa phosphoproteins, at 1 h for the 55- and 46-kDa phosphoproteins, and at 2 h for the 55-, 46-, and 22-kDa phosphoproteins. The 46- and 55-kDa phosphoproteins are putative structural proteins, and the 22-kDa phosphoprotein is proposed to be a protein kinase C substrate previously identified in Hermissenda following multitrial classical conditioning. Time-dependent increases in protein phosphorylation may contribute to the induction and maintenance of different memory stages expressed in sensory neurons after one-trial conditioning.     

Targeting of glycoprotein I (gE) of varicella-zoster virus to the trans-Golgi network by an AYRV sequence and an acidic amino acid-rich patch in the cytosolic domain of the molecule.

Previous studies suggested that varicella-zoster virus (VZV) envelope glycoproteins (gps) are selectively transported to the trans-Golgi network (TGN) and that the cytosolic domain of gpI (gE) targets it to the TGN. To identify targeting signals in the gpI cytosolic domain, intracellular protein trafficking was studied in transfected cells expressing chimeric proteins in which a full-length or mutated gpI cytosolic domain was fused to the gpI transmembrane domain and interleukin-2 receptor (tac) ectodomain. Expressed protein was visualized with antibodies to tac. A targeting sequence (AYRV) and a second, acidic amino acid-rich region of the gpI cytosolic domain (putative signal patch) were each sufficient to cause expressed protein to colocalize with TGN markers. This targeting was lost when the tyrosine of the AYRV sequence was replaced with glycine or lysine, when arginine was replaced with glutamic acid, or when valine was substituted with lysine. In contrast, tyrosine could be replaced by phenylalanine and valine could be substituted with leucine. Mutation of alanine to aspartic acid or deletion of alanine abolished TGN targeting. Exposure of transfected cells to antibodies to the tac ectodomain revealed that the TCN targeting of expressed tac-gpI chimeric proteins occurred as a result of selective retrieval from the plasmalemma. These data suggest that the AYRV sequence and a second signaling patch in the cytosolic domain of gpI are responsible for its targeting to the TGN. The observations also support the hypothesis that the TGN plays a critical role in the envelopment of VZV.